This invention relates to an improved tufting machine configuration for the tufting of carpet with a relatively low pile and a relatively high pile with the relatively low pile areas being substantially more uniform than has heretofore been achieved. The resulting carpet is particularly well suited for tip shearing the relatively high pile sections.
The tufting of multiple pile height carpet patterns is well known in the tufting industry and has been accomplished through a variety of techniques, most generally pattern control yarn feed mechanisms of roll type or scroll type attachments. Most recently, such pattern attachments have been driven by computer controlled servo motors as described in Taylor, U.S. Pat. No. 4,867,080 and most preferably by independent servo motor controlled pattern attachments such as is described in the assignee's co-pending Ser. No. 08/980,045.
Traditionally, when tufting multiple pile height carpet, the yam carrying needles are set to penetrate backing fabric by an equal depth and to be seized upon loopers at an equal depth below that backing fabric. The difference in pile height is obtained by relatively underfeeding the yarns to the low pile height areas and thereby backrobbing some of the yam tufted for those stitches. Backrobbing is an inherently non-uniform process as it involves not only the elasticity of a particular section of yam, but also the varying resistance encountered by that yam as it is pulled through the backing fabric. The result is that slight variations in pile height occur and these variations are exaggerated the more the yam must be backrobbed to produce a low pile height. Such variations make it difficult to closely tip shear the relatively higher pile height yams without also tip shearing some of the irregular lower pile height yams. Thus a method of more uniformly tufting lower pile height yams is desired.